This invention relates to an apparatus for the production of foam for the purpose of fire prevention and suppression.
For some time foaming agents have been used to increase the effectiveness of water in the prevention and suppression of fires. Systems have traditionally used foaming agents, commonly known as surfactants, mixed in holding tanks or introduced into the water stream by a variety of methods. More recently systems have been developed which also provide for the injection of compressed air into the water/surfactant mixture to provide an improved quality and volume of foam.
In U.S. Pat. No. 5,582,776 of the present inventors issued Dec. 10th 1996 is disclosed a portable apparatus for generating foam. The apparatus disclosed was particularly directed at an apparatus for making compressed air foam to be used in stationary or portable fire fighting systems and emergency response units. The system is particularly applicable to portable systems used in forestry, structure protection, rural and urban grass fires (Class A fires), and oil and gas fires (Class B fires).
The arrangement shown in the above patent was particularly designed as a portable unit for use in remote locations. However attention is necessary to provide a more enhanced unit which can more effectively control the supply of foam of a required characteristic particularly for use in situations where the foam must be more accurately controlled for different characteristics of the fire to be controlled.
It is one object of the present invention to provide an improved apparatus and method for generating foam which is more convenient for the operator and allows simple control of the system to generate the required characteristic of foam consistently.
According to one aspect of the invention there is provided an apparatus for generating foam comprising:
a source of compressed air under pressure arranged, when actuated, to provide a stream of the compressed air at a predetermined rate;
a pump for pumping a liquid to be foamed having a pump inlet for connection to a liquid supply and a pump outlet;
a supply line connected to the pump outlet for receiving a flow of the liquid therefrom;
an injector connected into the supply line and arranged for supplying to the supply line a quantity of a foaming agent from a foaming agent supply proportional to the flow of liquid so as to be incorporated therein;
a mixer for feeding the liquid and the foaming agent incorporated therein from the supply line into the stream of compressed air and for mixing the liquid, foaming agent and compressed air to generate the foam;
and a control valve for controlling the rate of flow of the liquid in the supply line to the mixer comprising:
a continuously variable valve member movable between a fully open position, in which a maximum flow rate of the liquid is supplied to the mixer with the proportional quantity of a foaming agent from the foaming agent supply, and a fully closed position, in which the flow of liquid and the flow of a foaming agent from the foaming agent supply are halted, and continuously variable therebetween;
a motor for driving the valve member between the fully open and fully closed positions;
an electronic control for controlling operation of the motor, the electronic control having a plurality of set positions corresponding to set positions of the motor and the valve member;
the set positions including the fully open position, the fully closed position and at least three intermediate positions.
According to a second aspect of the invention there is provided a method for generating foam comprising:
providing a stream of compressed air at a predetermined rate;
pumping a liquid to be foamed from a liquid supply and supplying the liquid at a pump outlet;
providing a supply line connected to the pump outlet for receiving the flow of the liquid therefrom;
providing an injector connected into the supply line and supplying to the supply line from the injector a quantity of a foaming agent from a foaming agent supply proportional to the flow of liquid so as to be incorporated therein;
providing a mixer for mixing the liquid and the foaming agent incorporated therein from the supply line into the stream of compressed air to generate the foam;
and controlling the rate of flow of the liquid in the supply line by:
providing a continuously variable valve member movable between a fully open position, in which a maximum flow rate of the liquid is supplied to the mixer with the proportional quantity of a foaming agent from the foaming agent supply, and a fully closed position, in which the flow of liquid and the flow of a foaming agent from the foaming agent supply are halted, and continuously variable therebetween;
driving the valve member between the fully open and fully closed positions by a motor;
and controlling operation of the motor by an electronic control, the electronic control having a plurality of set positions corresponding to set positions of the motor and the valve member;
the set positions including the fully open position, the fully closed position and at least three intermediate positions.
As the amount of foaming agent is added in direct proportion to the amount of water, the valve may be used to control the flow rate of only the water, in which case the foaming agent is added downstream of the valve; or the foaming agent is added upstream of the valve and the valve used to control the flow rate of the mixture.
Preferably the electronic control includes a display for displaying to an operator the set position selected. This can be a screen or a series of LEDs.
Preferably the display displays the fully open position, the fully closed position and for each of the intermediate positions information relating to the wetness characteristics of the foam.
On one arrangement, the electronic control includes a single switch which is manually operable repeatedly such that each operation acts to cycle from one set position to the next. Alternatively, a series of individual switches can be used each associated with a respective one of the set positions and each having a respective display LED.
Preferably, when the valve is moved to the fully open position, the stream of compressed air is halted and a form and amount of foaming agent suitable for non-compressed air foam is used.
Preferably the three intermediate set positions are determined by measuring a rate of liquid flow from the valve member and by adjusting the respective set position to provide a predetermined flow rate.